In, for example, compact disc players, an optical scanning device scans the helical data tracks of a so-called compact disc (CD) by means of a light beam. Using an objective lens, the light beam is focused onto the CD by a focusing regulation circuit. A tracking regulation circuit guides the optical scanning device such that the light beam is always guided along the data tracks of the CD.
Unfortunately, scratches or contamination on the disc, such as dust or fingerprints, impair the reproduction of the recorded information, e,g., music. If the light beam arrives at a point which is contaminated, for example, by dust or a fingerprint, it may run uncontrolled over a number of the data tracks because the data are no longer readable and because the tracking regulation circuit may not reliably generate a regulating signal in the contaminated region of the disc. As soon as the light beam resumes scanning a clean (uncontaminated) data track on the disc, the tracking regulation circuit determines whether the light beam is still focused on the desired data track. Typically it will be displaced by a few data tracks radially inwards or outwards, The tracking regulation circuit now calculates and generates a regulating signal so that the light beam returns to the desired data track to be scanned.
Data located between the point where the light beam left the desired data track and the point to which it is returned is not reproduced. An interruption in the playback of the music can still be avoided within a CD player if the lost data can be bridged over by interpolation. However, if the contaminated or damaged spot on the disc is too large, then the listening enjoyment may be spoiled by a disturbing interruption.
Therefore, it is the object of the invention to design a method whereby data loss caused by contaminated or damaged spots on the recording medium is as small as possible.